Bleaching composition and method



United States Patent 2,988,514 BLEACHING COMPOSITION AND METHOD Homer L. Robson, Lewiston, N.Y., Lorenzo D. Taylor,

St. Petersburg, Fla., and Richard R. Heinze, Ransomville, N.Y., assignors to Olin Mathieson Chemical Corporation No Drawing. Filed June 11, 1958, Ser. No. 741,216

25 Claims. (Cl. 252--187) This invention relates to improvements in bleaching using acid solutions of a chlorite.

In the bleaching of cellulosic materials, including particularly pulp and textile, an acid solution of a chlorite is commonly used to obtain maximum bleaching and the production of goods of high whiteness. A typical bleach bath used in textile work contains, for example, approximately one gram per liter of sodium chlorite. Sufficient acid is added to the bath with or without buffering to bring the pH to the desired value, generally to a pH of about 3.5 for cotton goods or about 2.5 for polyacrylonitrile fiber. Acetic acid is the preferred acid for achieving the pH of 3.5 and formic acid is the preferred acid for achieving the pH of 2.5. Phosphoric acid is also frequently used as an acidifying agent. Bufifer salts, for example, Na HPO NaH PO or NH HF can be added. In addition, wetting agents which are effective under acid conditions, for example, the lgepons (salts of acylalkyl taurides) are commonly added. Bleaching baths of these compositions are commonly used at elevated temperatures, for example 180 F. to 195 F.

Under these conditions of use, the bleaching solutions generate chlorine dioxide rather rapidly, as evidenced by the development of a' yellow color in the solution and by the evolution of chlorine dioxide as a gas from the surface of the solution. This'generation of chlorine dioxide is objectionable in that the gas lost from the solution represents'a loss in bleaching power. It is also objectionable as a health hazard when sufficient chlorine dioxide is evolved to aflect workers deleteriously. Chlorine dioxide is an irritating gas and requires removal, for example, by means of hoods from the working space. Furthermore, acid chlorite solutions, particularly when chlorine dioxide is being evolved in the range of pH 2 to pH 4, are corrosive to stainless steels and other metals. These metals become pitted and then corrode at a faster rate than the original highly polished surfaces. In addition, the corrosion products in the solution frequently stain the textile and accelerate further decomposition of the chlorite to chlorine dioxide. Thus, it is necessary, for the most economical and efficient bleaching, to acidify the bleaching bath to form chlorous acid and/ or chlorine dioxide at a rate matching the demand on the solution bythe textile being bleached and, at the same time, to avoid producing an excess of chlorine dioxide which would saturate the solution and be evolved as a gas.

- Fine adjustment of the pH of the bleaching bath is difficult and, by itself, is inadequate to provide sufiicient chlorine dioxide, as opposed to too much chlorine dioxide. Control of the rate of formation of chlorine dioxide has been attempted by starting the bleach at a moderate temperature, such as 160 F. and a moderate pH of about 4 and adding acid and increasing the temperature during the bleaching period to activate the remaining chlorite more strongly. But such procedures require constant manual attention and it is more desirable, in any event, to add sufficient acid at the beginning for the entire process and to maintain constant temperature.

Considerable control of the corrosion aspect of the excessive chlorine dioxide production problem can be efiected by addition to the bleaching bath of nitric acid as the acidifying agent or the addition to the bleaching bath of inorganic nitrates up to a molar ratio of 0.5/1

difiicult, since it has no buffering action. Consequently,

some mills have preferred to add nitrate salts, e.g., sodium nitrate, to the bath along with the other ingredients and to employ acetic acid as the acidifying agent. Acetic acid has a pronounced and useful buffering action, tending to hold the pH value somewhat constant or, at least, minimizing its rise as the bleach bath is used. The addition of sodium nitrate or other nitrate salts to the bathdoes not interfere with the buffering action. However, there is a limit to the ability of nitrates to retard corrosion of stainless steel in acidified chlorite solutions; to reduce the amounts of corrosion products, particularly iron compounds which cause the decomposition of the chlorite and the production of chlorine dioxide; and to overcome the adverse effects of, for example, iron which may be introduced into the bleach bath from other sources.

Thus, it is seen that there are needed means and methods which repress excessive evolution of chlorine dioxide in baths containing all the necessary acid at the beginning of the bleaching operation. One such method of repressing the formation of chlorine dioxide with hydrogen peroxide is described in US. Patent No. 2,358,866, issued September 26, 1944, to J. D. MacMahon. US Patent No. 2,526,839, issued October 24, 1950, to R. N. Aston, describes the use of pyrophosphates and polyphosphates alone or with hydrogen peroxide for the same purpose. However, hydrogen peroxide and the polyphosphates are effective in acid solutions having a pH of about 3 and inordinately large amounts of these repressers are required at lower pH levels. Consequently, what have been sought are more effective and more economical repressers in the pH 2 to pH 3 range to lessen decomposition of the chlorite and formation of chlorine dioxide. Such repressers would be assisted by the use of nitrates to reduce the amounts of corrosion products, particularly iron compounds, in the bleach baths.

A principal object of the present invention is to provide an acidic aqueous bleach bath in which the active bleaching agent is supplied in the form of a water-soluble chlorite and in which there are additionally contained novel repressers which are particularly effective in preventing the formation of chlorine dioxide in such amounts as will cause the evolution thereof from the bath as a gas and which act without interfering with the bleaching action of the bath.

Another object of the present invention is to provide a concentrated aqueous composition suitable for addition to an acidified aqueous bleach bath to produce a buffered solution which is substantially non-corrosive to stainless steel and which contains the novel repressers. The active bleaching agents in the bath are supplied in the form of water-soluble metal chlorites.

A third object of the present invention is to provide a concentrated, stable, solid composition suitable for addie liter of sodium chlorite are used, but, in some circumstances up to 20 grams per liter or more can be used. Equivalent amounts of LiCIO KClO or Ca(ClO can also be used. I

The novel repressers employed are polyamides of the general formula:

NH CH CHR NH) H in which R is hydrogen or methyl and n is 1 to 4. Ethylene diamine is a particularly preferred represser and is conveniently introduced into the bleaching bath as the dihydrochloride. Other amines within the scope of the formula are diethylene triamine, triethylene tetramine, tetraethylene pentamine, propylene diamine, dipropylene triamine, and other propylene homologues of these polyamines, and mixtures thereof, The hydrochlorides or phosphate salts of these amines are useful forms in which the amines may be obtained, handled and introduced into the bleaching bath.

Manyqamines repress the formation of chlorine dioxide from acidic chlorite solutions. However, they may form inactive chloroamines which have no bleaching action or they may be so reactive as to reduce the active bleaching agents in the solution and rob it of available oxidizing power. Again, other amines form colors which are objectionable in a bleaching process. By contrast, the polyamines of the formula NH (CH CHR NH) I-I where R is H or methy and n is 1 to 4 are very effective in repressing the formation of chlorine dioxide in the aqueous acidic chlorite solutions at pH values from the neutral point of 7 to as low as about 2 without these adverse effects. The proportions of polyamine required are suitably in the range of 10 to 1000 parts per million by weight in a bleaching bath containing about 1000 to 2000 parts by million by weight of sodium chlorite or equivalent amounts of other water-soluble chlorites. Observable effects begin at about 10 parts per million by weight of the polyamine and more than about 500 parts per million by weight appear to be of no additional advantage over somewhat smaller amounts. The proportion of represser is related, as described, to the chlorite content of the bleaching bath and is varied with the chlorite content, so as to maintain the proportion set forth. And, in such proportion, these polyamines are surprisingly effective in repression, particularly when compared with other nitrogen-bearing compounds and with other proposed repressers, even in the presence of known accelerators of chlorine dioxide formation. Triethylene tetrarnine, for example, represses chlorine dioxide formation, even in the presence of 2 parts per million by weight of iron, though not as well as it does in the absence of iron.

Thus, when using the polyamines defined above in the presence of dissolved iron, there may be some loss of total efi'ective bleaching power in the bath. Ordinarily, this is not excessive unless the proportion of iron is excessive and, if iron is absent, there is substantially no loss of bleaching power. If the polyamines combine in any Way with the active bleaching agents, the products are also active bleaching agents. They reduce the formation of chloride or chlorate from the c-hlorite and thereby preserve the bleaching power of the chlorite. They do not form any colored lay-products which might interfere with bleaching textiles to high whiteness. They are stable and effective re'p'ressers at operating temperatures between room temperature and the boiling point of the solution. They are compatible with other components of the bleaching baths.

In addition to the chlorite, the acid and the polyamines discussed above, the bleaching bath of the present invention advantageously contains conventional ingredients. such as butters, corrosion inhibitors, wetting agents and metal ion ohelating agents. Suitable buffers include, for

example, Na 'HPO N'aH PO NH HF sodium acetate,

4 and acetic acid. 'Ihese buffers tend to keep the pH of the solution constant in spite of the introduction of materials tending to neutralize the acid, raise the pH, and thereby reduce or stop the bleaching action.

In bleaching textiles with acidified chlorite solutions, wetting agents stable and effective in such solutions are commonly added to the bleaching bath. When sodium chlorite was introduced to the textile trade, a study was made of the various wetting agents which might be used. Members of the Igepon (salts of acylalkyl taurides) series were found to be the most satisfactory of those tested. The lgepon T compounds (salts of higher acyl derivatives of lower alkyltaurides), particularly the oleoyl derivatives, are especially useful. Baths containing these wetting agents have somewhat longer life than those made with other wetting agents. Accordingly, Igepon T wetting agents wcre generally recommended to the textile trade for use with acidic chlorite solutions and many textile mills continue to employ them.

Equipment employed in bleaching textiles with chlorite is commonly made of stainless steel. The stainless steel may be combined with sheets of glass, Transite (a hard pressed, heavy board or tubing made from asbestos and Portland cement), and other inert materials. Particularly with intermittent use for chlorite baths, stainless steel may show some corrosion, sufficient to add one part per million by weight or iron to the bleach bath or a sutficient fraction of a part per million to affect the course of the bleaching adversely, e.g., by accelerating chlorine dioxide formation and evolution, by acting antagonistically toward the repressers, by introducing discoloration, and by damaging the equipment being employed. Nickel and cobalt which may be dissolved from the stainless steel act similarly to the iron in these regards. Again, these metals may appear in the bleaching bath due to corrosion or they may be otherwise, often inadvertently, introduced. Whatever their source, they are deleterious and their introduction is to be avoided if possible. Indeed, it is preferred in the practice of this invention to take positive steps to remove such metals if they have been introduced.

To reduce the corrosion of stainless steel and to prevent the introduction of deleterious metal ions therefrom into the bleaching bath, a water-soluble nitrate salt is preferably included in the bath. Ammonium nitrate and alkali metal and alkaline earth metal nitrates such as sodium nitrate, potassium nitrate, calcium nitrate or magnesium nitrate are preferably employed. A suitable proportion of up to about 0.50 mole of nitrate per mole of chlorite is used. Such proportions materially reduce corrosion and introduction of deleterious metal ions from stainless steel into the bleaching solution.

To inactivate traces of the deleterious metal ions which have been introduced, the bleaching solution can contain, in a preferred modification of the present invention, a chelating agent which is stable with respect to the bleaching components and effective in acid solution. A study of the eifect of iron on the repressing action of various amines showed that iron either weakened the repressing action or was itself so strong a catalyst in the formation of chlorine dioxide that, to obtain optimum repression, inactivation of the iron is required. In glass -equipment with iron completely absent, some repressers give good repression of the chlorine dioxide, resulting in long bath life and more even bleaching of the goods being treated. The same test made in metal equipment shows poor repression, due to a small pick-up of iron.

The chelating agents useful in the present invention are those amines havinga plurality of hydrogen atoms of the amino group replaced by fatty carboxylic acid groups. Particularly useful members of this group include ethylene diamine tetra-acetic acid, hydroxyethyl-ethylene diamine triacetic acid, iminodiacetic acid, nitrilo-triacetic acid, symmetrical ethylene-diamine diacetic ajcidand their salts, generally alkali metal salts, such as sodium salts.

Also. useful are citric, --maleic,-rlac.tic andtartaric acid and salts of citric acid and tartaric acid, for example, alkali metal salts such as sodium citrate and sodium potassium tartrate. These chelating agents are effective at the pH used in acidified chlorite bleaching baths to the action of iron and other metal ions, such as nickel and cobalt, in engendering the formation of chlorine dioxide. Ordinarily, about 5 to50 parts per million by weight, based on the solution'are satisfactory.

Thus, to summarize what has been said concerning the bleaching bath solutions ,of the present invention, these aqueous compositions include from about 0.1 and 20 grams per liter of sodium chlorite or equivalent weights of other water-soluble chlorites, are given a pH within the range of 2 to 7, and contain at least one polyamine of the formula NH, (CH CHR NH H in an amount sufficient to prevent the evolution of chlorine dioxide gas from the bath but insuflicicnt in amount to destroy the bleaching potential of the chlorite. R in the formula is selected from the group consisting of H and methyl and n is aninteger from 1 to 4. For all practical purposes, this means that the polyamines are present in proportions of about to 1000 parts per million by weight in baths containing about 1000 to 2000 parts per' million by weight of sodium chlorite or equivalent amounts of other chlorites. These solutions can also contain an alkali metal or an alkaline earth metal nitrate in an amount of up to 0.50 mole of nitrate per mole of chlorite to serve as a corrosion inhibitor and suitable amounts of buffering agents, wetting agents and chelating agents.

The aqueous concentrates within the ambit of the present invention differ from the bleaching baths discussed above in that they contain neither water-soluble chlorite nor acid. They contain an alkali metal or alkaline earth metal nitrate such as sodium nitrate, potassium nitrate, lithium nitrate or calcium nitrate and they contain a polyamine of the type previously discussed. Advantageously, they also contain a chelating agent. The proportion of each component in the mixture is adjusted to provide a composition which, when introduced into an acidified chlorite solution, provides a bleaching bath which is substantially non-corrosive to stainless steel, suitably repressed'with respect to chlorine dioxide formation and still efiective under normal bleaching operation conditions. To this end, the following composition is generally suitable:

Component: Percent by weight Nitrate 32 Polyamine 5-15 Chelating agent 3-10 Water Balance Where particularly low temperatures may be encountered, it is preferable to use about 30 percent by weight of the nitrate component to lower the freezing point. Where the nitrate is an alkaline earth metal nitrate, it is preferable to use about 8 to 10 percent by weight of the chelating agent to obtain clear concentrates.

The non-aqueous components of the concentrates of the invention are all readily soluble in water inthe recited proportions to form clear, stable solutions of a pH of about 11 to 12. The concentrates themselves freeze only below 0 F. and are easily prepared, stored,

and shipped. When diluted by addition to an acidifiedchlorite solution, these concentrates yield a bleaching bath which is effective, stable, substantially non-corrosive and does not generate obnoxious quantities, of chlorine dioxide. Suitable proportions are about 0.5 to 1.3 grams of the concentrate per gram of a commercial bleaching product containing from 80 to 84 percent by weight of sodium chlorite or an equivalent amount of another" water-soluble chlorite used in bleaching baths. Smaller proportions may protect only inadequately and greater amounts slow the bleaching process, although they do not impair the bleaching capacity of the bath. The concentrated aqueous compositions of the present invention are completely soluble in water and are effective represser s, especially at a pH of 2 to 3, without destroying bleaching power.

The solid compositions within the scope of the present invention differ from the bleaching baths discussed above in that they contain neither water-soluble chlorite, acid nor water. They contain an alkali metal nitrate such as sodium nitrate, potassium nitrate or lithium nitrate, but generally, they do not contain alkaline earth metal nitrates because of their hygroscopic nature. They contain a polyamine of the above noted formula, preferably in the form of a hydrochloride or phosphate salt. They also contain a buffering agent. Disodium phosphate is the preferred butler, but sodium dihydrogen phosphate, polyphosphates, e.g., tetrasodiumpyrophosphate and sodium tripolyphosphate, as well as ammonium bifluoride and sodium acetate, can be employed. These buffers tend to hold the pH constant when chlorine dioxide is formed according to the equation:

since they replace the acid in the solution. Advantageously, these compositions also contain chelating agents of the type discussed above. The proportion of each component in the mixture is adjusted to provide a com position which, when introduced into an acidified chlorite solution, provides a bleach bath which is non-corrosive to stainless steel, suitably repressed with respect to chlorine dioxide formation and still efiective in bleaching under normal operating conditions. To this end, the following composition is generally suitable:

Component: Percent by weight Nitrate 30 to 55 Buffer 25 to 50 Polyamine (or salt) 4 to 12 Chelating agent 3 to 20 These components are preferably finely ground and admixed in any suitable manner, as by ball-milling or tumbling, to form a homogeneous mixture. The solid composition of the present invention is readily soluble in water and is an effective represser, particularly at a pH of 2 to 3, without being destructive of bleaching power.

Within the following limits, the solid compositions, when dissolved in suitable proportions in an acidified chlorite solution, yield a bleaching bath which is effective, stable, substantially non-corrosive and does not generate obnoxious quantities of chlorine dioxide. Suitable proportions are about 0.5 to 1.0 gram of the solid per gram of a commercial bleaching product containing 80 percent by weight sodium chlorite used in the bleaching bath. Smaller proportions may protect only inadequately and greater amounts slow the bleaching process, although they do not impair the bleaching capacity of the bath. Larger proportions of nitrate in the composition are accommodated by decreasing the proportion of bufier. When the nitrate is in the 45 to 55 weight percent range, the proportion is reduced to about 0.5 gram per gram of sodium chlorite product, maintaining the molar ratio of nitrate to chlorite below about 0.50/1 in the bleach bath.

For a further understanding of the present invention, reference is made to the following examples:

Examples I-VIII A 'solution containing 860 parts per million by weight 7 of sodium chlo'rite was bulfered at pH 3.0 by the addition of 30 grams per liter of glacial acetic acid and 0.5 gram per liter of sodium acetate. It was divided into several portions to each of which was added a different of the solution was added 500 parts per million. by weight of triethylene tetramine. To another portion; 500 parts.

per million by weight of triethylene tetramine and2 parts proportion of a polyamine product having the following per million by weight of ferric chloride were added. A composition: third portion was used as a blank. The solutions were maintained at 88 C., removing samples from time to time g g d t weight i g and determining the parts per million by weight of chlop an wa er rine dioxide. After 30 minutes, the total content of soh a f dium chlorite and dissolved chlorine dioxide was detery enetetramme mined with the following results: Higher polyethylene polyamlnes 7.0

100.0 010:, ppm. 010, and NaClOa,

p.p.m. Each solution was maintained at 88 C. for various periods, removing a portion of the solution from time to Time, Min. No Re- With No Re- With time and chilling to stop further generation of chlorine Puss Empress Presser Repress dioxide. The content of dissolved chlorine dioxide in each sample in parts per million by weight was deter- 0 1 X2 :3 mined photometrically. When the concentration of free, dissolved chlorine dioxide had reached a fairly constant 0 0 0 0 860 860 860 value, the run was stopped. The ability of the poly- 6 130 0 22 amines to reduce materially the formation of chlorine 58111211111111: igg 3 dioxide and thus to prolong the life of the bath is clearly an 1'60 0 a 620 860 210 shown in the following table:

Example No I It III 1V V VI VII VIII Polyamlne,p.p.m 0 20 50 100 150 200 300 400 500 Chlorine Dioxide Produced, p.p.m.

Time in Minutes:

45 22 20 1s 1s 1s 1 0 22 18 1s 16 10 0 2s 1s 1s 16 10 0 1s 1s 10 10 p as s 1s 1d 10 0 22 1s 1s 10 o 25 1s 1s 10 o 30 1s 16 0 0 s5 40 22 1s 10 0 50 so 22- 14 s 70 to so 16 s so so 40 2o .10 130 20 so so a0 12 so so a0 16 so ls Example 1X These data show that the represser, in the absence of A solution containing 860 parts per million by Weight ron, substantially prevented the evolution of chlorine of sodium chlorite was buifered at pH 3 by adding an dwxlde, at t same'tlme preservms'the b a power acetic acid sodium acetate b ff To One portion f of the solution in the form of chlorine dioxide and chlonis solution was added 500 parts p61 million by weight 50 In e presence m y welsht of o e of ethylene diamine. Another portion was used as a represser still very effectively prevented the evolution of blank The Solutions were maintained at C remov chlorine dioxide, although the iron caused a considerable ing samples from time to time and determining the parts 0f total OXldlZmg P per million by weight of chlorine dioxide. After 30 minutes, the total content of sodium chlorite and dissolved 59 Example XI chlorine dioxide was deterrruned with the following A bleaching bath was made p containing 0.925 g results.

per liter of a commercial bleaching product contain ng 80 Weight per cent NaCIO equivalent to 1200 parts per @102 CIOwHdNaOIOW-W- 60 million by weight of available chlorine. Eight milliliters 'rlino, Min. N with N0 with of 56 weight percent aqueous acetic acid and 0.5 gram of Reprgssm. RepreSs-er Repressor Represser caustic soda were added per hter to adjust the pH to 3. Then 0.5 gram per llt'er of Igepon T-77 (sodlum salt 0 0 360 860 of oleoyl methyl tauride) Wetting agent was dissolved 5 in the solution. To one portion of this solution were 160 IIIIIIIIIILIIIIII: added 10 parts per mil-lion by weight of diethylenetriamine trihydrochloride and to another portion none was added. The solutions were heated to 86 C. for one These data show that the represser slowed considerably hour in the presence of a Sample of polyethylene tereph the P J gi s? e f 70 thalate fiber-cotton textile using 15 grams per 500 millii i i t f .3 5 6 so u m e 0 liters of bleach solution (solution to cloth ratio by weight, c e 1 i 33/1 The cloth originally had a brightness of 58, Example X measured using a Photovolt brightness meter. Chlorine .A solution containing 860 parts per million by weight 75 dioxide content o'f'the solution was determined on samples o'f's'odium chl'orite was buttered at pH 3 by the addition removed at intervals. At the end of one hour, the cloths 9 were removed, rinsed, dried; ironed and the brightness determined. Results are shown in the following table:

I Diethyiene triamine trihydrochlorlde.

In each of the pairs of tests, agreement is satisfactory. The data clearly show the repressive influence of the BETA. No significant difference appears in the brightnessof the bleached cloth.

Example XII A bleaching bath was made up containing 0.925 gram per liter of a commercial bleaching product containing 80 weight percent NaCl equivalent to 1200 parts per million of available chlorine. Eight milliliters of 56 weight percent aqueous acetic acid and 0.5 gram of caustic soda were added per liter to adjust the pH to 3. Then 0.5 gram per liter of Igepon T-77 wetting agent was dissolved in the solution. To separate portions of this solution were added various proportions of ethylene diamine dihydrochloride and to another portion none was added. The solutions were heated to 86 C. for one hour in the presence of a sample of polyethylene terephthalate fiber-cotton textile using 15 grams per 500 milliliters of bleach solution (solution to cloth ratio by weight, 33/ 1). The cloth originally had a brightness of 58, measured using a Photovolt brightness meter. Chlorine dioxide content of the solution was determined on'samplcs re moved at intervals. At the end of one hour, the cloths were removed, rinsed, dried, ironed and the brightness determined. Results are shown in the following table:

- Ethylenediamine dihydrochloride.

Where duplicate tests were run, agreement is satisfactory, The data clearly show the repressive influence of the ethylene diamine dihydrochloride. In each case, the chlorine dioxide content of the solution was reduced by increasing amounts of the polyamine. No significant difference appears in the brightness of the bleached cloth.

Example XIII This example shows the eifectiveness of one of the polyamines in repressing chlorine dioxide formation in the presence of 'iron using ethylene diamine tetra-acetic acid as chelating agent. a

A bleaching bath was made up containing 0.925 gram per liter of a commercial product containing 80 weight percent NaClO equivalent to 1200 parts per million of available chlorine. Eight milliliters of 56 percent aqueous acetic acid and 0.5 gram of caustic soda were added per liter to adjust the pH to 3. Then 0.5 gram per liter of Igepon T-77 wetting agent was dissolved in the solution. To separate portions of this solution were added various proportions of ethylenediamine dihydrochloride, ferric chloride and ethylenediamine tetra-acetic acid with suitable blanks. The solutions were heated to 86 C. for one hour in the presence of a sample of a polyethylene terephthalate fiber-cotton textile using 15 grams per 500 milliliters of bleach solution (solution to cloth ratio by weight, 33/1). The cloth originally had a brightness of 58, measured using a Photovolt brightness meter. Chlorine dioxide content of the solution was determined on samples removed at intervals. At the end of one hour, the cloths were removed, rinsed, dried, ironed and the brightness determined. Results are shown in the following table:

Experiment No 1 2 3 4 5 6 Iron, ppm 0 0 10 10 10 10 EDA, 2HCl, p.p.m 0 100 0 100 100 0 Chelating Agent, p.p.m 0 O 0 0 100 100 Bath Analysis, 010;, p.p.m.:

Time, Minutes- 15 48 20 76 64 16 48 30 70 34 100 88 24 70 60 100 64 100 88 48 76 Brightness of Bleached cloth 81. 7 80. 9 79. 8 79. 9 80. 7 81. 6

1 Ferric chloride added. b Ethylenediamine dihydrochloride. e Ethylcnediamine tetra-acetic acid sodium salt.

These data show the chlorine dioxide formation in No. l' in the absence of iron, polyamine or chelating agent. No. 2 shows repression of chlorine dioxide in No. l by addition or ethylenediamine dihydrochloride. No. 3 shows the accelerating eiiect on chlorine dioxide formation by the addition of iron. No. 4 shows the repression by the polyamine, even in the presence of iron. No. 5 shows the special benefit of polyamine and chelating agent together in repressing chlorine dioxide formation. No. 6 shows that the chelating agent alone is not wholly responsible for this improved result, but both the polyamine and chelating agent are necessary.

Example XIV This example shows the additional use of sodium. niirate in the bleach baths of the present invention.

A bleaching bath was made up containing 0.925 gram per liter of a commercial productcontaining 80 weight percent NaClO The pH was brought to 3 by the addition of acetic acid and 0.5 gram per liter of Igepon T- 77 wetting agent was added. Two portions of this solution were used as blanks. To each of two other portions were added 100 parts per million by weight of ethylenediamine dihydrochloride, 50 ppm. by weight of Versene (ethylene diamine tetra-acetic acid sodium salt) and 360 p.p.m. by weight of sodium nitrate. Swatches of a polyethylene terephthalate fiber-coton cloth weighing 15 grams were introduced into each solution, including the blanks and they were then stirred at C. for one hour. The swatches were removed and the brightness determined for comparison with the original brightness of 60.0. The following data were obtained:

Experiment N o 1 2 3 4 EDAJHCl, p.p.rn 0 0 100 Versene" b p.p.m 0 0 50 50 NaN0 p.p.m. O 0 360 360 G102, p.p.m 210 202 127 131 Brightness of cloth 79. 8 78. 9 7i). 4 80. 0

e Ethylenediamine dihydrochloride. b Ethylenediamine tetra-acetic acid sodium salt.

Example XV intervals spectrophotometrically. A blank was run without the propylenediamine and the following results were obtained:

Chlorine Dioxide, ppm.

With Repressor Time in Minutes No Repressor Example X VI A solution containing 860 parts per million by weight of sodium chlorite was buttered at pH 3 by adding an acetic acid-sodium acetate butler. A portion of this solution was used as a blank. To the remainder of the solution was added 500 parts per million by Weight of ethylene diamine. A portion of this solution was used in test No. 1. To the remainder of the solution was added 2 parts per million by weight of ferric chloride. A portion of this solution was used in test No. 2. To the remainder of the solution was added 400 parts per million by weight of citric acid. This solution was used in test No. 3. Each of the test solutions was maintained at 88 C. for 30 minutes, removing samples from time to time and determining the parts per million by weight of chlorine dioxide. The total content of chlorine dioxide and dissolved sodium chlorite was determined in the final sample. The following results were obtained:

C p.p.m. C10; and NaClO p.p.m.

l 2 3 Blank l 2 3 These data show that the represser, in the absence of iron (test No. 1), slowed considerably the evolution of chlorine dioxide, at the same time preserving the bleaching power of the solution in the form of chlorine dioxide and chlorite. The iron, even in the presence of the represser, materially accelerated the evolution of chlorine dioxide (to 400 p.p.m. by weight after 30 minutes) and destroyed much of the bleaching power of the solution (180 p.p.m. by weight combined chlorine dioxide and chlorite remaining after 30 minutes). Further addition of citric acid as chelating agent in test No. 3 overcame the effect of the added iron and even improved the action of the represser (only 22 ppm. by weight of dissolved chlorine dioxide after 30 minutes). The citric acid also preserved the bleaching power of the solution (800 parts per million by weight of chlorine dioxide and chlorite remained after 30 minutes).

Example XVII A solution containing 860 parts per million by weight of sodium chlorite was buffered at pH 3 by adding an acetic acid-sodium acetate buffer. A portion of this solution was used as a blank. To the remainder of the solution was added 500 parts per million by Weight of triethylene tetramine. A portion of this solution was used in test No. 1. To the remainder of the solution was added 2 parts per million by weight of ferric chloride. A portion of this solution was used in test No. 2. To the remainder of the solution was added 400 parts per million by weight of citric acid. This solution was used in test No. 3. 'Each of the test solutions was maintained 12 at 88 C. for 30 minutes, removing samples from time to time and determining the parts per million by weight of chlorine dioxide. The total content of chlorine dioxide and dissolved sodium chlorite was determined 'in' the final sample. The following results were obtained:

Blank 1 2 3 0 0 0 o 0 22 s 0 16 s 169 q s 14 160 0 a 8 These data show that the represser, in the absence of iron (test No. 1) substantially stopped the evolution of chlorine dioxide, at the same time preserving the bleaching power of the solution in the formo-f chlorine dioxide and chlorite. The iron, even in the presence of the represser (test No. 2), accelerated the evolution of chlorine dioxide (to 22 ppm. by weight after 5 minutes) and destroyed much of the bleaching power of the solution (210 p.p.m. by weight combined chlorine dioxide and chlorite remaining after 30 minutes). Further addition of citric acid as chelating agent in test No. 3 controlled the eifect of the added iron and preserved the bleaching power of the solution (790 parts per million by weight of chlorine A solution containing 860 parts per million by weight of sodium chlorite was buffered at pH 3 by adding an acetic acid-sodium acetate butler. A portion of this solution was used as a blank. To the remainder of the solution was added 500 parts per million by weight of triethylene tetramine. A portion of this solution was used in test No. 1. To the remainder of the solution was added 2 parts per million by weight of ferric chloride. A part of this solution was used in test No. 2. To the remainder of the solution was added 400 parts per million by weight of 'tartaric acid. This solution was used in test No. 3. Each of the test solutions was maintained at 88 C. for 30 minutes, removing samples from time to time and determining the parts per million by weight of chlorine dioxide. The total content of chlorine dioxide and dissolved sodium chlorite was determined in the final sample. The following results were obtainedf These data show that the represser, in the absence of iron (test No. l) substantially stopped the evolution of chlorine dioxide, at the same time preserving the bleaching power of the solution in the form of chlorine dioxide and chlorite. The iron, even in the presence of the represser (test No. 2), accelerated the evolution of chlorine dioxide (to 22 ppm. by weight after 5 minutes) and de stroyed much of'the bleaching power of the solution (210 ppm. by weight combined chlorine dioxide and chlorite remaining after 30 minutes). Further addition of tartaric acid as chelating agent in test No. 3 controlled theeifect of the added iron and improved retention of the bleaching power of the solution (380 parts per million by weight-of chlorine dioxide andychlorite remained after- 30 minutes) 1 Example XIX An aqueous concentrate of the following composition l 14 were removed, rinsed, dried, ironed and the brightness again measured. The following results were obtained:

was p p Test No 1 2 3 4 i 6 Concentrate added: Component 7 igfig m ./1 0.5 0. 7a 1.0 Fins iii 4g Chlorine iriii'dfb'iiiii? assassin... is 0 0 0 Q Ethylenediamine tetracetie acid sodium salt $8 i 0 35 25 23 waten H r 55 minutes. 0 65 50 4s 7 60 1111uutes. 9O 95 90 9.) 100 Brightness 88.0 86.2 86.2

A bleach bath was prepared by dissolving 0.9 gram Example XXI P li of this and g P liter of a 9- A concentrate of the following composition was premel'mal Product FQIltalIllllg l Naclo: 111 pared by dissolving the following components in water water. The addition of milllhters of 56 percent acem h propel-Hons mdlcated; tic acid per liter of solution brought the pH to 3.0. A swatch of a polyethylene terephthalate fiber-cotton was 20 O t P t b introduced into a solution having a solution/cloth weight omponen $51211: y ratio of 30/1 and the mixture was stirred at 85 C. for one hour with a stainless steel stirrer. The chlorine dig c d iu m ntrata so 11 am ll) 3 content of ihe olutlon was detennlned photomet- Ethy lgngdiamir lg tetra-acetic acid sodium salt; 5 ncally from time to time and at the end of one hour the Water 55 swatch was removed, rinsed, dried, ironed and the brightm ness determined using a Photovolt brightness meter with l msmnulus greep filter (ongmal bnghmess 600) A bleach bath was prepared by dissolving 1.0 gram per A blank was run omitting the aqueous concentrateof the liter of a comer Ci a1 product containing 80 weight s gg g iggz f and the followmg comparatwe results cent NaClO in water, adding ferric chloride to provide 5 parts per million by weight of iron. To separate portions of this solution were added varying amounts of the Chlorine dloxide,p,p m 31ml; wi h concentrate described above reserving one portion as a dime 85 blank. Each portion was adjusted to a pH of 2.5 by the addition of a mixture of 2 volumes of concentrated 2 v 2 nitric acid to 1 volume of glacial acetic acid andswatches 30minute8::::::: 120 40 of a polyacrylonitrile fiber cloth were introduced (solumminu 165 70 tion to cloth weight ratio, 30/1). Original brightness, Brightness Cloth 80 so I determined using a Photovolt brightness meter and a tristimulus green filter was 83. The solutions were The data show that chlorine dioxide was maintained at stm'ed 115mg a WP? stamless Fteel j at all times at a materially lower level in the bath with addifor 1 detefmmmg the chlonne dloxlde content of tive but the same bleaching effect was obtained in the h 501M101! at lntervals- At f of one hour the same time 7 cloths were removed, rinsed, dried, ironed and the brightness again measured. The fiollowing results were ob- Example XX mined: An aqueous concentrate was prepared by dissolving the following components in water in the proportions indi- Test 1 2 3 4 cated: 60 oonce n t rate added: 1 0 5 0 75 1 0 0 0.6 0.9 1.2 Component Pewrcqngby 2.9 2.4 2.5 2.5

408 72 98 98 Sodium mum a0 so mlnutes III: 380 115 115 115 Ethylene rll l0 mlnutes 310 140 130 130 gglitylene diamine tetra-acetic acid sodium salt 5g Brightness 86.1 88.3 87.5 87.1

100 W The data show good pH control, material repression of 60 chlorine dioxide formation even at this pH and excellent A bleach bath was prepared by dissolving 1.0 gram per bleachmgliter of a commercial product containing 80 weight per- Example XXII g z ii fi g f l l t g g t0 lz Another aqueous concentrate suitable for use accordp P In! on Y 8 0 0 SeParae P ing to the present invention was made by dissolving 23 1 263332 cigg qg d sggvz gzgemglg gni g r gzn g z the following components in the proportions indicated:

r1 blank. Each portion was adjusted to pH 3.0 by the addition of acetic acid and a swatch of a polyacrylonitrile fiber Compment gif gfi fi cloth was introduced into the solution (which has a solution to cloth weight ratio of 30/1). Original brightness, Calcium nitrate 20 determined using a Photovolt brightness meter and a m ieneanmiijjiiijjjIIIIZIIIIIIIIIIIIIIIIIIIIIIIIII 10 stimulus green filter was 83. The solutions were stirred ggg tetra-acetic acid 306mm salt 2 using a type 316 stainless steel stirrer at 85 C. for l '7 hour, determining the chlorine dioxide content of the so' lution at intervals At the end of one hour the cloths Example XXIII An aqueous concentrate was prepared by dissolving the following components in water in the proportions indicated:

Component Percent byweight Sodium nitrate 30 Ethylenediamine 10 Ethylenediamine tetra-acetic acid sodiumsalt.- Water V 55 Total Q. 100

A bleach bath was. prepared by dissolving, 1.0 gram per liter of 94 weight 'percentcalcium chlorite in water. To

separate 500 milliliter portions of thissolution were. added,

varying amounts of the concentrate described above, reserving one portion as a blank. Each portion was adjusted to pH 3.5 with 56 weight percent acetic acid, then heated to 85 C. for one our. through the solution during this time to sweep out the chlorine dioxide into a potassium iodide solution. At the end of one hour the total available chlorine and the chlorine dioxide remaining in the solution, the chlorine dioxide swept out, and the pH were determined. The following results were obtainedi The data show that the composition of this invention materially reduces chlorine dioxide evolution from calcium chlorite solution and. maintains goodipH control.

Example XXIV The following solid compositionwas prepared :v

Each component was finely ground and the mixture was homogenized by tumbling.

A bleach bath was prepared by dissolving one gram per liter of a commercial product containing 80 weight percent NaClO and one gram per liter of the above composition in water. Formic acid was added to bring the pH to 2.5 and the solution was heated to 85 C. It was stirred and maintained at that temperature for one hour in contact with swatches of a polyethylene terephthalate fiber-cotton cloth (solution to cloth weight ratio, 30/1) and with a test piece of type 316 stainless steel. Chlorine dioxide content of the solution was determined from time to time and at the end of one hour the swatch was-re moved, rinsed, dried, ironed and the brightness determined using a Photovolt brightness meter with a tristimulus green filter (original brightness, 60.0). A'blank was run omitting the'solid'repressor' compositionofthe-- Nitrogen was bubbled 1-6 present invention and the following comparative results were obtained:

Blank 3 With additive Chlorine dioxide, p.p.m.:

O minut 0 0 15 minutes 125. V 100,

30 minutes 150 130 60 minutes 160 150. Brightness of cloth 81 The data show that chlorine dioxide was maintained at all times at alower level iii thebatliwith additive but the same bleaching eifect was obtained in the same time.

Example XXV A bleach bath was prepared; by dissolving one: per. liter of 'a commercial product containing 80 weight.

end of one hour the swatch was removed, rinsed, dried,

ironedand the brightnessdetermined using a'Photovolt brightness meter 'with a tristirnulus green filter (orig inal brightness,r60.0). A blank was run omitting .the solid repressor composition of the present invention and the followingcomparative-data were obtained:

Blank With additive Chlorine dioxide, p.p.m.:

0 minutes The 'data show .very substantial repression of chlorine dioxide formation without any interference with the eifectiveness of the bath in bleachings.

Example XXVI A bleach bath was prepared by dissolving one gram per liter of 'a commercial product containing 80 weight percent Nac1o,', ferric chloride to provide 3 parts per million by weight of dissolved iron per liter and one gram per'liter' of the solid composition of Example" XXIV. Acetic acid was added to bring the pH to 3. A swatch of a polyacrylonitrile fiber cloth was added (solution to cloth weight ratio, 30/1) and the mixture was stirred at 85 C. for one hourwith a type 316 stainless steel stirrer. The cloth had an original brightness of 83 measured using a Photovolt brightness meter with a tristimulus green filter. Chlorine dioxide content of the solution was determinedon samples removed at intervals. At the end of one hour, the cloths were removed, rinsed, dried, ironed and the brightness determined asbefore. A blank w'asrun omittingthe' solid repressor composition of the present invention. The-following results were obtained:

. a ,17 chlorine dioxide formation. The bleach was improved over the blank without the represser composition.

Example XXVII A bleach bath was prepared by dissolving one gram perliter of a commercial product containing 80 weight percent NaCIO ferric chloride to provide 3 parts per million by Weight of dissolved iron per liter and one gram per liter of the solid composition of Example XXIV. A mixture of two volumes. of concentrated nitric acid and one volume of glacial acetic acid was added to bring the pH of the solution to 2.5. Swatches of polyacrylonitrile fiber-cloth were added (solution to cloth ratio, 30/1) and the mixture was stirred at 85 C. for one hour. The cloth had an original brightness of 83 measured using a Photovolt brightness meter with a tristimulus green filter. Chlorine dioxide content of the solution was determined on samples removed at intervals. At the end of one hour, the cloths were removed, rinsed, dried, ironed and the brightness determined as before. A blank was run omitting the solid represser composition of the present invention. The following results were obtained:

These data show maintenance of constant pH and low chlorine dioxide formation. The bleach was improved over the blank without the represser composition.

Example XX VIII The following solid composition was, prepared by mixing the finely ground components:

Component Percent by Weight Sodium nitrate Disodium phosphate Ethylenediamine dihydrochloride. Ethylenediamine tetra-acetic acid sodium salt Total.

A bleach, solution was prepared by dissolving in-water at 60 C., 17.2 grams of the above composition and 17.2 grams of a commercial product containing 80 weight percent NaClO to make each liter of solution. Thesolution was acidified to pH 3.8 by the addition of acetic acid. To one portion of the solution was added several swatches of cotton cloth using a solution to cloth weight ratio of 9:1. Another portion was tested without cloth. A third solution contained 17.2 grams per liter of a commercial product containing 80 weight percent NaClO acidified with acetic acid to pH 3.8, but containing no represser composition or cloth. All three solutions were maintained at 60 C. for 45 minutes. A stream of nitrogen was passed over each solution at 200 milliliters per minute. The chlorine dioxide was absorbed from the gas stream in acidified potassium iodide solution and the liberated iodine was titrated at the end of 45 minutes using standard sodium thiosulfate solution. The sweepgas from the solution without represser contained 25 parts per million of chlorine dioxide, while the sweepgas from the solutions containing the represser composition contained only 5.1 and 4.1 parts per million of chlorine dioxide from the solutions with and without cloth, respectively.

Example XXIX A composition was prepared by mixing 6 grams of ethylene diamine with 30 grams of sodium dihydrogen phosphate monohydrate.

The mixture was moistened with one milliliter of water and stirring was continued while the mixture heated to 98 C. On cooling, the composition was ground and further mixed with. 19 grams of disodium phosphate and 5 grams of ethylene diamine tetra-acetic acid sodium salt. The mixture was reground and then combined with 40 grams of sodium nitrate, ground again. The resulting powder was stable, odorless and suitable for use in acid chlorite solutions.

Example XXX A bleach bath was prepared by dissolving one gram per liter of 94 percent calcium chlorite and one gram per liter of the solid composition of Example XXIV in water. Acetic acid was added to bring the pH to 3.5. The solution was heated to C. and stirred for one hour. A stream of nitrogen sweeping over the surface at 200 cc./min. swept all chlorine dioxide released into a trap containing aqueous potassium iodide. At the end of one hour the chlorine dioxide dissolved in the solution, the chlorine dioxide swept off, and the total available chlorine in the solution were determined. A blank was run omitting the composition of this invention and the following comparative data were obtained:

Blank With.

Additive Available chlorine:

In a1, p.p.m 1, 535 l, 535 Final, p.p.m 775 1, 055

010 swept out, p.p.m v 47 0101 in solution, p.p.m 34 71 Total 0102 evolved 179 118 The data show that the composition of this invention in an amount sufiicient to prevent the evolution of chlorine dioxide gas from the bath but insuflicient in amount to destroy the bleaching power of the chlorite, R being selected from the group consisting of hydrogen and methyl and n being an integer from 1 to 4.

2. The aqueous acidic bleaching bath of claim 1 wherein the water-soluble metal chlorite is an alkali metal chlorite.

3. The aqueous acidic bleaching bath of claim 1 wherein the water-soluble metal chlorite is sodium chlorite.

4. The aqueous acidic bleaching bath of claim 1 wherein the polyamine is ethylene diamine.

5. The aqueous acidic bleaching bath of claim 1 V of at least one polyamine of the formula metal chlorite and the polyamine is ethylene diamine.

6. The aqueous acidic bleaching bath of claim .1 wherein the water-soluble metal chlorite is sodium chlorite and the polyamine is ethylene diamine.

V wherein the polyamine is triethylene tetramine.

9. The aqueous acidic bleaching bath of claim 1 wherein the polyamine is dipropylene triamine.

10. The aqueous acidic bleaching bath of claim 1 in which the pH range is from 2 to 4.

11. The aqueous acidic bleaching bath of claim l in which the polyamine is present in the proportionof to 1,000 parts per million by weight per: 1,000 to 2,000

parts per million by weight of sodium chlorite.

12. An aqueous concentrate suitable for use in an aqueous acidic chlorite bleaching bath having an acid pH within the range of from 2 to 7, said chlorite being a water-soluble metal chlorite selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites, said concentrate consisting essentiallyof 20 to 32 weight percent of at least one compound selected from the group consisting of alkali metal nitrates and alkaline earth metal nitrates, 5 to 15 weight percent R being selected from the group consisting of hydrogen and methyl'and n being an integer from 1 to 4, 3 to 10 weight percent of a chelating agent for deleterious metal ions and which is stable with respect to the metal chlorite 'and effective in the acid bath, and a balance of water.

13. The aqueous concentrate of claim 12 wherein the compound selected from the group consisting of alkali 15. The aqueous concentrate of claim 12 wherein the chela ting agent is ethylene diamine tetra-acetic acid. a 16. The aqueous concentrate of claim'12 wherein the compound selected from the group of .alkali metal nitrates and alkaline earth metal nitrates issodium nitrate,

the polyamine is ethylene diamine and the chelating;

agent is ethylene diamine tetra-acetic acid. I

17. A solid composition suitable for use in an aqueous I acidic chlorite bleaching bath having an acid pH within the range of from .2 to 7,-said chlorite being: a watering of alkali metal chlorites and alkaline earth metal chlorites, said composition consisting essentially of 30 to 55 weight percent of at least one alkali metal nitrate, 25

-to,50 weight percent of-a buiferingagent, 4 to 12 Weight percent of at least one polyamine of the, formula i R being selected from the group consisting of hydrogen and methyl and n being an integer from 1 to4, and 3 soluble metal chlorite selected from the group consistto 20 weight percent of a chelating agent for deleterious metal ions and which is stable tothe me'tal chlorite and efiective'in the acid bath. 7 V

18. The solid composition of claim 17 wherein the alkali metal nitrate is sodium nitrate. 5 j v 19. The solid composition of claim 17 whereinthe l'nlifering agent is disodium phosphate. a

'20. The solid composition of claim 17 wherein the polyamine is ethylene diamine hydrochloride.

21. The solid composition of claim 17 wherein th chelating agent is ethylene diamine tetraacetic acid.

22. The solid composition of claim 17 wherein the alkali metal nitrate is sodium nitrate, the buifering agent is disodium phosphate, the polyamine is ethylene diamine, and the chelating agent is ethylene diamine tetraacetic acid.

23. In the use of an aqueous acidic chlorite bleaching bath having an acid pH within the range of from 2w 7,

said chlorite being a water-soluble metal chlorite selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites, the method of repressing the generation of chlorine dioxide in the bath which comprises including in the bath at least one polyamine of the formula pH range of from 2 to 4.

25. The method'of claim 23 in which the polyamine is included'in the bath in the proportion of 10 to 1,000 parts per million by weight per 1,000 to 2,000 parts per million by weight of sodium chlorite.

References Cited in the file of this patent UNITED'STATES PATENTS 1,748,494 Murrill Feb. 25, 1930 2,377,066 Baird et al. May 29, 1945 2,499,987 Clapham Mar. 7, 1950 2,526,839 Ashton Oct. 24, 1950 2,711,363 Waibel June 21, 1955 2,739,882 Ellis Mar. 27, 1956 12,740,689 Easton et al. Apr. 3, 1956 2,810,717 Lamborn Oct. 22, 1957 2, 36,566 Duncan May 27, 1958 2,850,461 Bloch et al. Sept. 2, 1958 FOREIGN PATENTS 507,997 Canada Dec. 7, 1954 1 OTHER REFERENCES Versenes: Tech. Bull. No. 2, sec. II, pp. 6-10, 16, 17, ub. by Bersworth Chemical Co., Framingham, Mass. .(1952). 

1. AN AQUEOUS ACIDIC BLEACHING BATH HAVING AN ACID PH WITHIN THE RANGE OF FROM 2 TO 7 AND CONSISTING ESSENTIALLY OF WATER, A WATER-SOLUBLE METAL CHLORITE SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL CHLORITES AND ALKALINE EARTH METAL CHLORITES, AND AT LEAST ONE POLYAMINE OF THE FORMULA 